Film guiding assembly

ABSTRACT

A film guiding assembly for guiding a plastic film during travel along a desired path includes at least two non-rotating turning bars over which the film passes, and an actuator for pivoting the turning bars to laterally shift the film. A sensor for senses the lateral position of the film downstream of the turning bars and operates to cause the actuator to pivot the turning bars when necessary to maintain the film leaving the guiding assembly in the desired path.

RELATED APPLICATION

This application claims priority from U.S. Provisional Patent Application No. 60/903322 filed Feb. 26, 2007.

FIELD OF INVENTION

The present invention relates to film guiding assemblies for guiding plastic film during travel along a desired path.

BACKGROUND OF THE INVENTION

It is frequently necessary to guide plastic film as it travels along a desired path. Guiding techniques currently used usually comprise a set of rollers which pivot to change the direction of the film. However, this often produces a change in film tension, with resulted tension memory in the film. Such tension memory can cause problems further along the path of travel. For example, if the film is subsequently wound on a roll and the tension of the film during winding is not sufficient, the edge of the roll may follow the film memory so that the roll edges are not straight. Edge guides which utilize such techniques therefore tend to create the same problem which they were designed to eliminate.

SUMMARY OF THE INVENTION

The present invention provides a film guiding assembly for guiding a plastic film during travel along a desired path, the assembly including:

-   -   at least two non-rotating turning bars over which the film         passes;     -   an actuator for pivoting the turning bars to laterally shift the         film; and     -   a sensor for sensing the lateral position of the film downstream         of the turning bars and operable to cause the actuator to pivot         the turning bars when necessary to maintain the film leaving the         guiding assembly in the desired path.

The film therefore slides over the turning bars. The turning bars may be lubricated by a gas such as air for use with sticky films or films with a high coefficient of friction or may have a slippery coating. It has been found that such an arrangement guides a plastic film without causing any substantial additional stress in the film such that, if the film is subsequently wound onto a roll for example, the film in the roll is subsequently without tension memory.

The actuators may also be operable to move the turning bars to a loading position in which the film can be passed therebetween in a downward direction. Further, the guiding assembly may include further actuators operable to permit the turning bars to rotate during a start-up operation.

BRIEF DESCRIPTION OF THE DRAWINGS

One embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, of which:

FIG. 1 is a diagrammatic side view of a film guiding assembly in accordance with one embodiment of the invention;

FIG. 2 is a diagrammatic front view of the turning bars in a non-angled orientation;

FIG. 3 is a similar view showing the turning bars in a first angled orientation;

FIG. 4 is a similar view showing the turning bars in a second angled orientation;

FIG. 5 is similar to FIG. 1 but shows how the guiding assembly is oriented to initially pass the plastic film therethrough;

FIG. 6 is a similar view showing the guiding assembly in an intermediate position between the orientation shown in FIG. 5 and the orientation shown in FIG. 1; and

FIG. 7 is similar to FIG. 1 but shows how the turning bars can be permitted to rotate during start-up.

DESCRIPTION OF PREFERRED EMBODIMENT

Referring to the drawings and as shown in FIG. 1, a plastic film 10 passes successively around two non-rotating turning bars 12, 14 of a film guiding assembly. In the orientation shown in FIG. 1, each turning bar 12, 14 reverses the direction of travel of the film 10. The turning bars 12, 14 are carried by a pivotable bar carrier 16. After leaving the turning bars 12, 14, the film 10 travels past an edge sensor 18 and then around a pair of guide rollers 20, 22. The bar carrier 16 is pivotable about an axis 24 by an actuator 26 controlled by an electrical controller 27 which receives an edge position signal from the edge sensor 18. The turning bars 12, 14 are air lubricated by air blowers 28, 29 which supply air under pressure through flexible ducts 30, 32 to the interior of the turning bars 12, 14. The turning bars 12, 14 have passages 34, 35 which feed air from the interior of the turning bars to their surfaces over which the film 10 passes. Alternatively, the turning bars 12, 14 may have low friction surfaces. The guiding assembly also includes a pair of actuators 36, 38 which are operable to permit or prevent rotation of the turning bars 12, 14, as will be described in more detail later.

The various parts of the guiding assembly referred to above will of course be appropriately secured to a suitable main frame, as will be readily apparent to a person skilled in the art.

FIG. 1 shows the guiding assembly in an operative position in which the actuators 36, 38 are actuated to prevent the turning bars 12, 14 from rotating, as is the case when film 10 is running through the guiding assembly.

FIG. 2 shows the turning bars 12, 14 in a neutral position. FIG. 3 shows the turning bars 12, 14 in a first angled position when it is desired to shift the film 10 laterally by a distance A, and FIG. 4 shows the turning bars 12, 14 in a further angled position when it is desired to shift the film 10 laterally by a distance B.

When the film 10 is initially being threaded through the guiding assembly, the actuators 36, 38 are operated to permit the turning bars 12, 14 to rotate, see FIG. 7. Initially, the actuator 26 is operated to cause the carrier 16 to pivot about axis 24 from the position shown in FIG. 1 to the position shown in FIG. 5. As shown in FIG. 5, the leading end of the film 10 can then easily be pulled downwardly between the turning bars 12, 14 and passed around rollers 20, 22.

The actuator 26 is then operated to return the carrier 16 back to the position showing in FIG. 1. FIG. 6 shows an intermediate position during this operation, during which turning bars 12, 14 can rotate to facilitate the operation. When the carrier 16 has returned to the position shown in FIG. 1, actuators 36, 38 permit rotation of the turning bars 12, 14 during start-up, as shown in FIG. 7. After start-up, actuators 36, 38 are again actuated to prevent rotation of the turning bars 12, 14, as shown in FIG. 1.

The advantages of the invention and other embodiments thereof will now be readily apparent to a person skilled in the art, the scope of the invention being defined in the appended claims. 

1. A film guiding assembly for guiding a plastic film during travel along a desired path, said assembly including: at least two non-rotating turning bars over which the film passes; an actuator for pivoting the turning bars to laterally shift the film; and a sensor for sensing the lateral position of the film downstream of the turning bars and operable to cause the actuator to pivot the turning bars when necessary to maintain the film leaving the guiding assembly in the desired path.
 2. A guiding assembly according to claim 1 wherein the actuator is also operable to move the turning bars to a loading position in which the film can be passed therebetween in a downward direction.
 3. A guiding assembly according to claim 1 including further actuators operable to permit the turning bars to rotate during a start-up operation. 